1. Field of the Invention
The present invention relates to an X-ray tube for generating X-rays.
2. Related Background Art
An X-ray tube has an electron gun comprised of a cathode, heater, grid electrode, and the like, a focusing electrode, and an anode target in a high-vacuum sealed housing (tube). The cathode is heated by the heater to emit electrons from the cathode. The electrons are focused through the grid electrode and focusing electrode to become incident on the anode target to which a high voltage is applied, thereby generating X-rays.
In the assembly of the X-ray tube, the position (position in the electron traveling direction) of the electron gun is determined by inserting the electron gun in the housing to oppose the focusing electrode integrated with the housing, and the lid portion which is opposite to the cathode of the electron gun is fixed to the housing, so that the housing is sealed.
In the X-ray tube, an electron beam from the electron gun must be focused to about 10 xcexcm on the anode target so that predetermined X-rays are obtained. In order to obtain this predetermined focal diameter, the distance between the focusing electrode and the grid electrode of the electron gun must be set to a predetermined distance highly precisely.
In the X-ray tube described above, when the electron gun is inserted in the housing to oppose the focusing electrode, the housing is closed with the lid portion of the electron gun, and accordingly the actual distance between the grid and focusing electrodes cannot be measured or inspected. It is therefore very difficult to set the distance between the grid and focusing electrodes to the predetermined distance highly precisely by positioning adjustment of the electron gun, and positioning adjustment of the electron gun takes a very long period of time. For example, if the grid electrode is displaced by about 100 xcexcm from the predetermined distance, the predetermined focal diameter (about 10 xcexcm) cannot be obtained.
It is an object of the present invention to solve the problems described above and to provide an X-ray tube in which the grid electrode can be positioned in the axial direction (direction along which electrodes line up) precisely and easily, so that an improvement in quality and reduction in assembly cost can be realized.
In order to solve the above problems, according to the present invention, there is provided an X-ray tube in which a cathode is heated in a housing sealed in vacuum to emit electrons, and the electrons are focused on an anode target through a grid electrode and a focusing electrode, thereby generating X-rays, characterized by comprising a spacer with one end fixed to the grid electrode and the other end abutting against the focusing electrode, the spacer being formed cylindrical so the electrons directed from the grid electrode toward the focusing electrode can pass therethrough.
In the X-ray tube according to the present invention, because of the presence of the spacer formed cylindrical so it does not block the electrons directed from the grid electrode toward the focusing electrode, and with one end fixed to the grid electrode and the other end abutting against the focusing electrode, the distance between the grid electrode and focusing electrode is set to a predetermined distance. The grid electrode can accordingly be positioned in the axial direction (direction along which electrodes line up) correctly and easily. As a result, an improvement in quality of the X-ray tube and reduction in assembly cost can be realized.
Also, in order to solve the above problems, according to the present invention, there may also be provided an X-ray tube in which a cathode is heated in a housing sealed in vacuum to emit electrons, and the electrons are focused on an anode target through a grid electrode and a focusing electrode, thereby generating X-rays, characterized in that the grid electrode has a plate-shaped base portion with an opening, at a center thereof, through which the electrons pass, and a cylindrical portion integrally molded with the base portion from the same material as that of the base portion, formed cylindrical so the electrons directed from the opening toward the focusing electrode can pass therethrough, and having one end abutting against the focusing electrode.
In the X-ray tube according to the present invention, the distance between the base portion of the grid electrode, which has the opening through which the electrons from the cathode pass and forms a microelectron lens for obtaining a predetermined focal point, and the focusing electrode is set to a predetermined distance by the cylindrical portion of the grid electrode, which is formed cylindrical so as not to block the electrons directed from the opening of the base portion toward the focusing electrode and integrally molded with the base portion so the end thereof abuts against the focusing electrode. Therefore, the base portion (microelectron lens) of the grid electrode can be positioned in the axial direction (direction along which electrodes line up) correctly and easily. As a result, an improvement in quality of the X-ray tube and reduction in assembly cost can be realized.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.